1. Field of the Invention
The invention concerns non-efflorescing cementitious mortar compositions in the form of a dry-mortar composition or an aqueous mortar composition, and use thereof, particularly as a decorative coating material.
2. Description of the Related Art
For traditional cementitious decorative coating materials such as color plaster, tile grout and powder paint, efflorescence is a familiar phenomenon which influences the finishing decoration effect. It is well known that calcium hydroxide produced during portland cement hydration is the source of efflorescence. Calcium hydroxide is easy to be delivered by water to the decorative material surface and will deposit as white crystalline color after water dries, which can further react with ambient carbon dioxide to form white calcium carbonate. Those white substances unevenly distributed on the color decorative material surface will affect esthetic decoration quality.
There are some methods known in the state of art to reduce or avoid efflorescence: To use low alkaline binder such as calcium sulfoaluminate cement or calcium aluminate cement which produces little or no calcium hydroxide. The use of active fillers, for example the use of reactive silica filler which reacts with calcium hydroxide with formation of calcium silicate. This reaction will consume calcium hydroxide so that efflorescence can be reduced or avoided. A sealing method, wherein the surface of a decorative coating is sealed by applying a film of an aqueous polymer emulsion material is also known.
JP 2000-302520 A discloses cement-based joint fillers with effectively controlled efflorescence, which are based on various cement materials, reactive silica acid filler, water-soluble amino resin, and an aqueous polymer dispersion or water-redispersible polymer powder.
In GB 2360769 A a non-efflorescing cementitious body is formed from portland cement, calcium aluminate cement, Ca-sulfate (e.g. gypsum), and reactive silica (e.g. blast furnace slag). Reactive silica means non-crystalline SiO2, which is in a metastable phase and can slowly react with the cement hydration by-product Ca(OH)2 to form hydrated calcium silicate.
Such a composition has serious disadvantages, particularly if it is applied as a thin layer decorative coating: Its adhesion, adhesion strength, and scratching resistance are very low. Because of water evaporation and substrate absorption, fresh thin layer coating will dry too fast after it is applied to the substrate, even though thickening and water retention agents are added. Since some mixing water is kept in thin layer mortar, the degree of cement hydration in early stages is very low. The reaction between the potential reactive filler and calcium hydroxide is also limited.
In JP-A 60-251162 a mortar composition for decorating building walls is described containing a polyacrylate dispersion, which shows no efflorescence.